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 Post subject: 1955 Zenith TV Tuning
PostPosted: Nov Mon 20, 2017 11:00 pm 
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Hi All,

I'm currently rounding the corner to finish a TV restoration. I have replaced all of the electrolytics and many of the paper caps. I also tested most of the tubes and have replaced the ones that were obviously bad. I'm very close on the picture but am looking for a little guidance on what I should try next.

Here's one picture of the tv with a digital antenna signal with a ghost image:

Image

and here's one with about as close as I can get the picture. Just a little more turning radius on the vertical adjustment and I'd be there:

Image

Any thoughts appreciated!

craig.


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 Post subject: Re: 1955 Zenith TV Tuning
PostPosted: Nov Mon 20, 2017 11:40 pm 
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From what I can see it looks like you have something going on with the horizontal.
Does this set use a horizontal AFC diode? If so I would check there. Bad Horiz osc tube can cause things like this too.

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 Post subject: Re: 1955 Zenith TV Tuning
PostPosted: Nov Tue 21, 2017 12:15 am 
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Joined: Apr Sat 06, 2013 2:18 pm
Posts: 308
Location: New Hampshire
Horz osc is way off freq.
1) try horz osc tube.
2) be sure you used the right value caps in the horz osc.
3) dont remember on these but newer Zeniths all used a coil for hoz hold.
It has a stop on it that is a sleeve you pull out to rotate further. Be sure the slug is about in the
middle of the coil.
If you keep turning it one way you will get one normal pix. The opposite way will give you
more pictures side by side..........

Zeno 8)
LFOD !


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 Post subject: Re: 1955 Zenith TV Tuning
PostPosted: Nov Tue 21, 2017 1:05 am 
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Location: Dallas, TX
cvsolfari wrote:
Hi All,

Here's one picture of the tv with a digital antenna signal with a ghost image:

Any thoughts appreciated!

craig.

I'm not sure what you mean by "digital antenna with a ghost image". Are you using a digital converter in the first picture? I don't see how you would get a ghost image that way. Maybe you mean you are getting a double image, maybe a sync problem.
Double check the capacitor values in the horizontal and vertical sections.

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"Excellent!" I cried. "Elementary," said he. - Sherlock Holmes


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 Post subject: Re: 1955 Zenith TV Tuning
PostPosted: Nov Tue 21, 2017 7:40 am 
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Location: Redlands CA
What Zeno said above is good advice.

This is a Horizontal problem, if the coil slug has to be adjusted all the way in or out to get it that close but it still won't quite lock in then you may have the wrong value cap across the Horizontal Oscillator coil or a drifted resistor in that circuit.


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 Post subject: Re: 1955 Zenith TV Tuning
PostPosted: Nov Tue 21, 2017 8:37 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1541
Location: Lafayette, CO
My 2 cents....that horizontal coil sings at that particular resonant frequency, with a cap across it. That piece of it looks fine. There are going to be one or two feedback loops comparing frequencies, any difference will show as a correction to bring the oscillator on frequency. The comparison is the pair of face-to-face diodes. Your problem is an adjustment of the coil or some imbalance in the wiring around the diodes. Craig


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 Post subject: Re: 1955 Zenith TV Tuning
PostPosted: Nov Wed 22, 2017 10:18 pm 
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Location: Allendale, NJ
You said you replaced many of the paper caps. I would replace all the paper caps.


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 Post subject: Re: 1955 Zenith TV Tuning
PostPosted: Nov Thu 23, 2017 1:07 am 
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Yes, definitely replace all the remaining paper caps, including any plastic-coated paper caps (see https://antiqueradio.org/recap.htm ).

If those 60+ year-old paper caps aren't leaky now, they will be soon. You don't want to "finish" a restoration and then keep hauling the TV back onto the workbench over and over, as the remaining caps give up the ghost.

If you still have the same symptom at that point, then I'd take Eric's advice and look closely at resistors in the horizontal circuits, as well as mica caps in those circuits. Although mica caps are generally more reliable than paper, they fail fairly often in sweep circuits, where they take more abuse than in other sections.

Regards,

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html


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 Post subject: Re: 1955 Zenith TV Tuning
PostPosted: Nov Sat 25, 2017 6:28 pm 
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Thank you to everyone for the great advice. After reviewing all the suggestions and looking at the circuits, I found a more than order of magnitude wrong capacitor that I installed. After correcting that, I then went through the low resistance (<1kOhms) resistors and found a few that were more than 30% off. One was double the markings.

Once I made all these changes and replaced a tube, I'm in very good shape:

Image

Image

Now I can watch all my favorite sports while working on projects in my workshop. Thank you everyone for helping! If you notice anything that can be improved in the picture, please let me know. I feel that the image is slightly off-center and will take a look at the bullseye setting, assuming no one tells me to stay away from that!

cheers.

craig.


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 Post subject: Re: 1955 Zenith TV Tuning
PostPosted: Nov Sat 25, 2017 8:35 pm 
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Well the color is a little weak. :)

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 Post subject: Re: 1955 Zenith TV Tuning
PostPosted: Nov Sun 26, 2017 2:03 am 
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Location: New Hampshire
Tom Schulz wrote:
Well the color is a little weak. :)


Good one Tom LOL !
Back in the 70's I did some contract work for a shop that did a lot of big box
warranty work. You wouldnt believe how many B&W TV's came in with the
complaint of "No Color".

73
Zeno 8)
LFOD !


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 Post subject: Re: 1955 Zenith TV Tuning
PostPosted: Nov Sun 26, 2017 6:19 am 
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cvsolfari wrote:
I feel that the image is slightly off-center and will take a look at the bullseye setting, assuming no one tells me to stay away from that!
Your screen geometry looks pretty decent at a glance, but if you want to tweak it, look in your manual for adjusters with names like vertical height, horizontal width, vertical and horizontal centering, vertical linearity, horizontal linearity. Not every TV has all those adjusters, so work with what you've got. You can't harm your TV by messing a little with these adjustments, unless you pound an adjuster with a sledgehammer.

Note that these adjustments are somewhat interactive:

-- height and vertical linearity
-- width and horizontal linearity

For example, turning the vertical linearity adjuster may somewhat affect the height, and vice versa. If you go back and forth between the two, making small changes, you'll soon see how they interact.

Linearity defines whether the picture is stretched (vertically or horizontally) in one half of the screen versus the other half. The following screen shows a TV with pretty good linearity:

Image

The squares in the top row are about the same height as those in the bottom row, showing good vertical linearity. The squares in the far left column are about the same width as those in the far right column (good horizontal linearity).

The circle in the pattern also helps you judge linearity. The next photo shows a different TV with poor vertical linearity. The top part of the screen is stretched vertically, making the circle somewhat egg-shaped:

Image

If you don't have a dedicated TV pattern generator, you can go to this website and make a DVD with various TV test patterns:

http://techpreservation.com/dvddl/testdisc.htm

Regards,

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html


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 Post subject: Re: 1955 Zenith TV Tuning
PostPosted: Nov Mon 27, 2017 11:33 pm 
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Location: Pewaukee, WI
cvsolfari wrote:
Now I can watch all my favorite sports while working on projects in my workshop. Thank you everyone for helping! If you notice anything that can be improved in the picture, please let me know. I feel that the image is slightly off-center and will take a look at the bullseye setting, assuming no one tells me to stay away from that!

cheers.

craig.


IIRC the Zenith "bullseye" was a tuner setting (to adjust channel fine tuning)....It will have NO effect on scan centering/geometry.


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 Post subject: Re: 1955 Zenith TV Tuning
PostPosted: Nov Tue 28, 2017 7:13 am 
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If the bullseye gizmo is a fine tuner, there's no harm in trying it out. No expertise required -- just let your eyes and ears tell you when the picture and audio are at their best (from a tuning standpoint).

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html


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 Post subject: Re: 1955 Zenith TV Tuning
PostPosted: Dec Tue 05, 2017 3:38 pm 
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Thanks for the tips on fine tuning, everyone. This is very helpful and I see a very small bit of deformation at the top so I'll play around with this. That image for visually seeing the stretching is great. Now I have to find a DVD player. Since I have a chromecast attached, I suppose that I could just stream a still picture from youtube: https://youtu.be/po_hBMtTaDg?t=2m5s

I'll post a few photos after I complete the test.

cheers,

craig.


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